Re: Weevely PHP Backdoor - Rule Proposal

[Martin Holste <mcholste () gmail com>]

Interesting stuff, nice write-up on the blog.  On the rules:
Limit the content to just the HTTP header by adding the "http_header"
modifier after the content match.
Don't use nocase, as base64 encoding is case-sensitive, so we want
exact matches.
Add on the restriction that we must have "&ei=" as a URI param to
anchor the match.
Add on the restriction that Google must be in the header, but make
sure we don't match on that first because it will be so common.  We do
this by adding fast_pattern to the more unique match.

So you end up with a rule like this:
alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"Weevely
PHP backdoor detected (system() function used)";
flow:to_server,established; content:"&ei=QHN5c3Rl"; http_header;
fast_pattern; content:"http://www.google.com/url?sa=";; http_header;
reference:url,bechtsoudis.com/security/put-weevely-on-the-your-nids-radar;
classtype:web-application-activity; sid:100001; rev:1;)

That kit definitely has a subtle backdoor, so these are good rules to
have--nice work!

On Sun, Nov 20, 2011 at 3:19 PM, Anestis Bechtsoudis
<bechtsoudis.a () gmail com> wrote:
> I work in the NOC team at a University Campus in Greece, and recently i
> have noticed a noticeable increase in web hacking incidents. In many of
> them the attackers used the weevely*1 php backdoor to maintain access to
> the hacked system.
>
> I have searched around the net for some relative snort rules but i
> didn't find a match. So i decided to write my own. I thought these rules
> might pose an interest to the community so i decided to share them in
> this list (see the attachment).
>
> A detailed analysis of how i concluded to these content patterns can be
> found in my blog post*2.
>
> I admit that i'm not a Snort expert, so any propositions are welcome.
>
>
> *1 http://code.google.com/p/weevely/
> *2 http://bechtsoudis.com/security/put-weevely-on-the-your-nids-radar/
>
> --
> ===============================================
> * Anestis Bechtsoudis                         *
> * Undergraduate Student                       *
> *                                             *
> * Network Operation Center (NOC Group)        *
> * Dept. of Computer Engineering & Informatics *
> * University of Patras, Greece                *
> *                                             *
> * Website: https://bechtsoudis.com            *
> ===============================================
>
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------------------------------------------------------------------------------
All the data continuously generated in your IT infrastructure 
contains a definitive record of customers, application performance, 
security threats, fraudulent activity, and more. Splunk takes this 
data and makes sense of it. IT sense. And common sense.
http://p.sf.net/sfu/splunk-novd2d
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